Abstract The UCLA Clinical Research Site (CRS) of the Multicenter AIDS Cohort Study (MACS) / Women's Interagency HIV Study (WIHS) Combined Cohort Study (CCS) proposes to continue to document clinical, immunologic, physiologic, behavioral, virologic, genetic and psychosocial changes in HIV?infected and ?uninfected men?who? have?sex?with?men (MSM). This includes proposed studies to document these changes in MSM recruited previously, as well as plans to recruit new untreated and recently treated HIV?infected MSM (primarily African? and Hispanic? Americans), to maintain the cohort. The UCLA CRS will provide leadership and participation in the working groups, CCS?wide and local studies and research publications, as well as collaborative multi? cohort studies, as it has since the inception of the MACS 35 years ago. The UCLA CRS has recruited a large team of early career and established co?investigators from a wide range of disciplines. These investigators have developed, and are continuing to develop, innovative proposals to advance our understanding of co- morbid conditions that arise in people living with treated HIV infection, as well as the pathophysiology, immunology, genetics and bio-behavioral characteristics of treated and untreated HIV infection. The breadth, enthusiasm, experience and innovation of the UCLA CRS investigators, combined with the experience and commitment of the long?term staff, and our leadership of several areas of HIV/AIDs research, will continue to play an invaluable role in the success of the CCS over the next seven years.